Index: src/OFStreamObserver.m
==================================================================
--- src/OFStreamObserver.m
+++ src/OFStreamObserver.m
@@ -44,10 +44,14 @@
 # import "OFStreamObserver_poll.h"
 #endif
 #if defined(HAVE_SYS_SELECT_H) || defined(_WIN32)
 # import "OFStreamObserver_select.h"
 #endif
+
+#ifdef _WIN32
+# include <ws2tcpip.h>
+#endif
 
 #import "OFInitializationFailedException.h"
 #import "OFOutOfRangeException.h"
 
 #import "autorelease.h"